An artist's conception of how the Baryon Oscillation Spectroscopic Survey (BOSS) -- the largest component of the third Sloan Digital Sky Survey (SDSS-III) -- uses quasars to measure the distant universe. Light from distant quasars is partly absorbed by intervening gas, which is imprinted with a subtle ring-like pattern. Astronomers now have measured the scale of this ring-like pattern with an accuracy of two percent -- a precise measurement of how fast the universe was expanding when it was just 3 billion years old.